The mechanisms of dispersal and the characteristics of dispersing mice of the subspecies Peromyscus maniculatus bairdi will be investigated in free-ranging populations. Monitoring natality and dispersal will be facilitated by providing the mice with optimal artificial habitats. These habitats will consist of aluminum cylinders, two meters in diameter, and contain nest sites, ample food and protection from predators. Mice will have free entry and exist through a single gate. There will be 16 sites with two habitat enclosures at each site and the distance between sites is approximately 40 meters. The age, sex, and familial relationships will be ascertained for all individuals moving within and between the 16 sites. One half of the habitats will be provided with a founding population consisting of a reproducing pair of mice. Under these optimal conditions, we predict that the parents will disperse more frequently than their offspring. By altering the conditions in these habitats (available food and nests sites, population density, experience of parents), the characteristics of the dispersants should change.